People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

Despite nationwide public health campaigns urging adolescents — and everyone, for that matter — to practice safe sex, some teens are still taking risks and ending up with sexually transmitted diseases (STDs). Among over 500 studies presented at the 2014 STD Prevention Conference on Tuesday, one of them found that the prevalence of chlamydia among young women is far higher than reported rates, in part, due to the fact that the disease often shows no symptoms.

STDs are among the trickiest diseases to put an end to because the viruses that cause them either remain dormant for an extended period of time before symptoms appear, or symptoms never appear at all. According to the Centers for Disease Control and Prevention (CDC), there are about 110 million infections in the U.S., with 20 million new ones each year. And although some of the worst, like HIV/AIDS, get the most attention, that doesn’t mean that others, like chlamydia, herpes, gonorrhea, syphilis, and hepatitis, aren’t prevalent.

In fact, the new study, conducted by the National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention (NCHHSTP), found that there is an overall prevalence of chlamydia in 1.7 percent of the population, which translates into 1.8 million infections among men and women aged 14 to 39. Only 1.4 million in infections are reported, however, meaning that way more people need to get tested. The CDC emphasizes the importance of getting tested if you have unsafe sex, but it places special importance in women getting tested. All sexually active women 25 and under should get tested annually, it says.

The reason women should get tested so often is because there’s a disproportionate prevalence of chlamydia in women, especially black women in the U.S. The latest report found that 6.4 percent of all adolescent girls, ages 14 to 19, had chlamydia, compared to only 2.4 percent of boys the same age. When race was accounted for, 18.6 percent of black adolescent girls had the STD compared to only 3.2 percent of white adolescent girls.

“Based on these findings, the authors stress the importance of screening all sexually active young females, according to CDC guidelines, to ensure that those who are infected get diagnosed and treated,” a press release for the study said. “They also note that substantial racial disparities highlight the need for targeted interventions, particularly to reduce the impact of chlamydia among young African-American women.”

There’s still so much left to do, but progress is being made. The “Get yourself Tested” STD awareness campaign is a collaboration between the American College Health Association, the Kaiser Family Foundation, MTV, the National Coalition of STD Directors, and Planned Parenthood Federation of America. Along with the chlamydia statistics, some results showing the impact of the campaign were also presented. Looking at only Cook County, Chicago, there was an overall 36 percent increase in April 2011 and 44 percent increase in April 2012 in STD testing, when compared to April 2010.

The importance of getting tested cannot be stressed enough. Although teens make up only 25 percent of the sexually-active population, they comprise half of all new STD infections. Getting tested, and knowing one’s status is one of the only ways to prevent the spread of STDs.